1. Field of the Invention
The present disclosure relates generally to printheads for evaporative printing of organic materials. More specifically, the disclosure relates to a MEMS printhead fabricated from an SOI material and assembled using backside solder connections for layering organic thin film onto a substrate by sublimation of ink.
2. Description of the Related Art
Organic optoelectronic devices, such as organic light emitting diodes (OLEDs) used for flat-panel displays, are fabricated by depositing layers of organic film onto a target substrate and coupling the top and bottom of the film stack to electrodes. Using advanced techniques, film layer thicknesses on the order of 100 nanometers can be achieved.
One such technique deposits OLED film layers onto substrate by thermal evaporation of the organic material from a thermal printhead. The organic ink material is first dissolved in a liquid carrier to form a liquid ink. The ink is transferred to the printhead, and the target substrate and printhead are drawn into close proximity. The ink is then heated in stages. The first stage evaporates the solvent. During the second stage, the ink is heated rapidly above its sublimation temperature until the organic ink materials evaporate to cause condensation of the organic vapor onto the target substrate. The process may be repeated until a desired film layer thickness is achieved. The composition of ink may be varied to achieve different colors and to optimize other properties such as viscosity and sublimation temperature.
High resolution OLED displays may require pixel characteristic dimensions on the order of 100 microns or less. To achieve this degree of quality control, the printhead gap, that is, the gap between the printhead and the target substrate should be specified on an order of magnitude commensurate with the desired pixel characteristic dimensions. MEMS technology has been proposed for fabricating thermal printheads for evaporative deposition having this level of precision. One of the problems to be solved with this approach, and which is addressed by the present disclosure, is how to deliver electrical energy to the printing surface of a MEMS thermal printhead while enabling a sufficiently small print gap.